Lighter-than-air craft for energy-producing turbines

ABSTRACT

A wind-based power generating system provides a wind energy converter for converting wind energy into another form of energy using a lighter-than-air craft configured to produce a positive net lift. The net lift includes both a net aerodynamic lift and a net buoyant lift. A tethering mechanism is configured to restrain the lighter-than-air craft with respect to the ground. The lighter-than-air craft defines an interior volume for containing a lighter-than-air gas, and the lighter-than-air craft has a fore section and an aft section. The tethering system has at least one attachment point on the fore section of the lighter-than-air craft and at least one attachment point on the aft section of the lighter-than-air craft. The lighter-than-air craft provides a stable aerodynamic moment with respect to a yaw axis about a center-of-mass of the lighter-than-air craft. The craft can be formed in a variety of aerodynamic profiles/shapes.

RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/565,916, filed Aug. 3, 2012, entitled LIGHTER-THAN-AIR CRAFTFOR ENERGY-PRODUCING TURBINES, the entire disclosure of which isincorporated herein by reference, which is a continuation-in-part ofco-pending U.S. patent application Ser. No. 12/579,839, filed Oct. 15,2009, entitled POWER-AUGMENTING SHROUD FOR ENERGY-PRODUCING TURBINES,now U.S. Pat. No. 8,253,265, issued Aug. 28, 2012, the entire disclosureof which is herein incorporated by reference, which claims the benefitof U.S. Application Ser. No. 61/105,509, filed Oct. 15, 2008, entitledAIRBORNE POWER AUGMENTING SHROUD FOR WIND TURBINES, the entiredisclosure of which is also herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a lighter-than-air craft forenergy-producing turbines. More particularly, the present inventionpertains to craft geometries that can provide with a stable flightplatform for energy-producing turbines.

BACKGROUND OF THE INVENTION

Though wind energy is increasingly popular, especially with the threatof global climate change, the cost of energy from wind farms is stillnot competitive with that of more conventional power sources.Additionally, most of the top-tier wind farm sites have already beentaken, forcing new developments to move to less favorable environmentswhich will make the large scale deployment of wind energy all butimpossible with current technology.

Windmills in recent years have become more effective and competitivewith other energy sources, but most still remain very expensive toinstall. As a result, their overall cost per installed kilowatt (kW) isstill high enough that they are only marginally deployed and contributeonly a small amount to the “electrical grid.”

The primary configuration of modern windmills is a horizontally-mounted,large diameter, three-bladed propeller that rotates at lowrevolutions-per-minute (rpm's) over a very large swept area. The higherthe rotational axis of the propeller can be mounted, the better, as thenatural speed of the wind increases with an increase in the height abovethe ground. Conventional windmills thus have very tall and very strongtower structures. Typically, they have a tubular steel tower that ismounted to a deep, subterranean cement base. The system has to be verycarefully engineered and sited appropriately for the surroundingterrain. The towers must maintain a central stairway or other means toallow construction and operator access to the upper mechanicals. Thetower must accommodate the heavy gearbox, electrical turbine, andpropeller assembly, as well as be strong enough to withstand gale forcewinds, and potentially earthquakes. To make the system even morecomplicated, the upper nacelle and gearbox/turbine housing must be ableto pivot on a vertical axis, so as to align the propeller correctly withthe wind direction at any time during the day or night.

On many windmill systems the individual blades of the windmill are ableto rotate about their individual longitudinal axis, for pitch control.They can optimize the pitch of the blades depending on the nominal windspeed conditions that are present at anyone time at the site. They canalso change the pitch of the blade to “feather” the propeller if thenominal wind speeds are too large. Occasionally the windmill is lockedto prevent rotation, and the blades feathered to prevent major damage tothe machine in a storm. All of this pitch control technology addssignificantly to the cost of windmills.

Another major disadvantage with conventional windmills is damage causedby lightning during thunderstorms. The blades can be upwards of 300 feetin the air and are a good source for lightning to find a conductive pathto the ground. Some of the more recently designed windmills use a systemof replaceable sacrificial lightning conduction attractors that arebuilt into each windmill propeller blade. They help channel thelightning away from the vulnerable composite structure that comprisesthe blade itself. The fact remains that one of the major causes ofwindmill downtime and maintenance costs are caused by lightning damage.

The size of many windmills is also a major problem for inspection,diagnostics, and repair. Often workmen have to use ropes and climbingtechniques to perform maintenance on the massive machines. It is veryexpensive and dangerous. In recent years workmen have fallen to theirdeath trying to repair the blades.

There have been a number of proposals for more efficient and/or costeffective means of harvesting the wind's energy in order to combat thehigh price of wind energy. There has been considerable effort put intodeveloping diffuser-augmented wind turbines, which have considerablyhigher power output for a given size rotor than conventional turbines.However, the cost of the diffuser has not justified their commercialimplementation.

Some effort has also been made to develop high-altitude wind harvesters,as high-altitude winds are considerably stronger than ground level windsand are present almost everywhere. In one example of this effort, it hasbeen proposed to provide tethered wind turbines that are deployed at orabove ground level. See US Published Application 20080048453 to Amick,the disclosure of which is incorporated herein by reference in itsentirety.

However, no conventional windmill yet addressees the foregoing problemswhile providing for cost-effective wind-energy production.

SUMMARY OF THE INVENTION

The present invention addresses problems encountered in prior artapparatus, and encompasses other features and advantages, through theprovision, in an illustrative embodiment, of a lighter-than-air (LTA)craft for an airborne wind-turbine for converting wind energy intoanother form of energy, the craft being disclosed in an illustrativeembodiment as a shroud having a ring-like shape having an airfoilcross-section and defining an interior volume for containing alighter-than-air (LTA) gas. For the shroud embodiment the shroudincludes a central opening oriented along a longitudinal axis of theshroud, and is further configured to produce an asymmetric moment ofleft and right lateral sections thereof, which asymmetric moment yieldsa restoring moment that automatically orients the longitudinal axis ofthe shroud substantially optimally relative to a prevailing winddirection. In addition to the shroud structure other geometries areconsidered as falling within the scope of the present inventionincluding, inter alia, craft that supports turbines or other mechanismsfor converting kinetic wind energy into other useful forms of energy.

In accordance with another feature of the present invention there isprovided a wind-based power generating system that includes a windenergy converter for converting wind energy into another form of energy;a lighter-than-air craft configured to produce a neutral or positive netlift to the wind energy converter, the net lift including a netaerodynamic lift and a net buoyant lift; and a tethering systemconfigured to restrain the lighter-than-air craft with respect to theground. The lighter-than-air craft defines an interior volume forcontaining a lighter-than-air gas, and the lighter-than-air craft has afore section and an aft section. The tethering system has at least oneattachment point on the fore section of the lighter-than-air craft andat least one attachment point on the aft section of the lighter-than-aircraft, and the lighter-than-air craft is constructed and arranged togenerate a stable aerodynamic moment with respect to a yaw axis about acenter-of-mass of the lighter-than-air craft.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention description below refers to the accompanying drawings, ofwhich:

FIG. 1 depicts an exemplary wind-turbine system incorporating theinventive shroud according to an illustrative embodiment;

FIG. 2 is a cross-sectional view of an exemplary shroud according to anillustrative embodiment of the present invention;

FIG. 3 is a vertical cross-sectional view of the exemplary shroud ofFIG. 2;

FIG. 4 is a diagrammatic vertical cross-sectional depiction of anexemplary shroud according to a further illustrative embodiment of thepresent invention;

FIG. 5 is a diagrammatic vertical cross-sectional depiction of anexemplary shroud according to a still further illustrative embodiment ofthe present invention;

FIG. 6 is a diagrammatic horizontal cross-sectional depiction of theinventive shroud illustrating the principle of operation of the shroudconfiguration producing the asymmetric moment of left and right lateralsections thereof;

FIG. 7 depicts another embodiment of the present invention with adifferent craft style;

FIG. 8 depicts an illustrative embodiment similar to that shown in FIG.7 but with added aerodynamic structures;

FIG. 9 depicts an illustrative embodiment similar to that shown in FIG.8 but with a different tether system;

FIG. 10 depicts an illustrative embodiment similar to that shown in FIG.8 but with still a different tether system;

FIG. 11 depicts a further illustrative embodiment of the presentinvention employing a novel craft having upper and lower wing sections;

FIG. 12 depicts still a further illustrative embodiment of the presentinvention employing a single wing section;

FIG. 13 depicts an embodiment similar to that shown in FIG. 12 butsupporting multiple smaller turbines; and

FIG. 14 depicts still another illustrative embodiment of the presentinvention employing a single wing section, but with no side walls orupper and lower wing sections.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like numerals refer to like orcorresponding parts throughout the several views, the present inventionis generally characterized as a lighter-than-air craft that can beconstructed and arranged as a power-augmenting or non-power-augmentingshroud for an airborne wind turbine for converting wind energy intoenergy (e.g., electrical energy), such as, for instance, an airbornewind-turbine of the type disclosed in above-incorporated US PublishedApplication 20080048453 to Amick.

In the following description reference is made to the use of alighter-than-air (LTA) shroud. Illustratively, FIGS. 1 and 2 depict sucha shroud arrangement. However, in other embodiments disclosed herein theturbines or other wind converters are illustrated as supported fromother structures, referred to herein generally as “craft”. For otherstructures refer, for example, to FIGS. 7-14.

The shroud 1 is a “lighter-than-air” (LTA) shroud, and is therebydimensioned to define an internal volume 2 capable of holding asufficient volume of lighter-than-air gas to provide buoyant lift forovercoming the weight of the airborne components of the wind turbinesystem comprising the “Lighter-than-air” (LTA) shroud, wind turbine andrelated components, and tether, and maintaining the wind turbine atheights substantially above ground level where wind speeds are generallyhigher (see FIG. 2). To this end, the material of the shroud ispreferably impermeable to egress of a suitable lighter-than-air gascontained therein, such as, by way of non-limiting example, helium, andis, furthermore, impermeable to ingress of outside air. According to theexemplary embodiment, fabrication and operation of the shroud canutilize materials, subsystems and processes such as those used in other“Lighter-than-air” (LTA) devices (e.g., aerostats). In the exemplaryembodiment, a mechanism is also provided for maintaining the volume oflighter-than-air gas at acceptable pressure, and further forsubstantially maintaining the shape and size of the shroud, in varyingatmospheric conditions. Such a mechanism can include, by way ofnon-limiting example, internal ballonets, subdividing the internalvolume of the shroud to define multiple internal compartments, etc.

Referring to FIG. 1, the shroud 1, along with all other associatedairborne components of the wind turbine system of which it is a part,can be lowered and raised from a base station 10 by employing a tether11. Any conventional mechanism, including such as disclosed, forexample, in Amick, US Publication Number 2008-0048453, can be employedto provide for the selective raising and lowering of the shroud 1 viathe tether 11.

Once airborne, the tethered shroud 1 passively floats downwind of thebase station. As wind direction changes, the drag force on the shroud 1,by virtue of its design as explained further herein, causes the shroud 1to passively change its location with respect to the base station 10,thereby automatically maintaining a down-wind position with respect tothe new wind direction.

Tether 11 is secured to shroud 1 at fore F and aft A attachment pointsso that the shroud's center of pressure is located downwind of thetether's fore F attachment points. Tether 11 is further attached to theshroud 1 at a location so that the aerodynamic forces on the shroud 1passively restore the minimum radius section thereof to be orientedapproximately normal to the direction of airflow. The passive stabilityand control of shroud 1 can, optionally, be further improved by movingthe shroud's center of pressure aft through the employment of aftstabilizers, such as flat winglets or fins (depicted as structures W inFIG. 1), on the exterior of shroud 1. Furthermore, the center ofbuoyancy and center of gravity of shroud 1 (taking into account the windturbine components disposed therein) are both located between the fore Fand aft A tether attachment points and as close to each other aspossible. Note that the wings (or where relatively small in reference tothe overall surface size—winglets) or fins on any of the embodimentsdescribed herein can be implemented in accordance with a variety ofarrangements. As shown, three wings or fins W are employed in atriangular orientation. Alternatively four or more wings or fins can beemployed in an appropriate geometrical arrangement (e.g. an orthogonallycrossing pattern of four fins, a pentagonal arrangement, etc.)

While capable of employment at a variety of scales, it is contemplatedthat shroud 1 can be dimensioned to accommodate wind turbines withminimum rotor diameters of approximately 5 to 10 meters (e.g. 6 meters),and is highly variable. Likewise, the number and arrangement of rotorblades is also highly variable.

Referring also to FIG. 2, the shroud 1 passively maintains the windturbine system approximately aligned with the direction of wind atheights above ground level, while increasing the power output of theenshrouded wind turbine by increasing the upstream size of the capturedstream tube 3 through aerodynamic diffusion of the airflow therethrough.To these ends, the shroud 1 is essentially characterized by a ring-likeshape the cross-section of which is an airfoil shape with (except wherethe airfoil is symmetric) the high-pressure surface 4 oriented towardthe shroud exterior and the low-pressure surface 5 oriented towards theshroud interior (the captured stream tube 3) with the chord oriented inthe direction of airflow at a geometric angle of attack (α_(geometric))equal to or greater than zero. According to the exemplary embodiment,the airfoil sectional thickness is in the range of from approximately12% to approximately 30%, while the chord/radius ratio is approximately1-5.

It is contemplated that, optionally, shroud 1 can further compriseadditional lift surfaces, such as wings W, disposed on the exterior ofshroud 1. Wings or winglets on any of the embodiments herein can extendapproximately horizontally from opposing sides of the craft and/or candefine a slight acute upward or downward angle (as shown in FIG. 1). Theterm “approximately horizontal” shall be deemed to include such acuteangles—e.g. up to an angle of approximately 20-40 degrees with respectto the horizontal plane perpendicular to gravity and parallel to theflat ground.

Still referring to FIG. 2, shroud 1 is further shaped such as to providea circular section (denoted by line 6) of minimum radius approximatelynormal to the wind flow and a divergent section downstream (i.e., aft ofthe wind turbine 20) thereof. The enshrouded wind turbine 20 is placedsuch that the turbine blades sweep out this minimum radius circularsection 6 as they rotate. The foregoing design passively augments thepower conveyed through the enshrouded wind turbine by increasing themass flow of air through the enshrouded wind turbine 20.

The drag force on shroud 1 increases parabolically as the wind speedincreases, and this additional force tends to lower the height of theshroud 1. Compensation against this drag force is provided for by anequivalent increase in lift force, and to this end shroud 1 is, in oneembodiment, shaped to provide additional lift force through positive netaerodynamic lift produced by utilization of high local lift airfoilsproximate the bottom 51 (relative to the base station) of shroud 1 andlow local lift airfoils proximate the top 52 (relative to the basestation) of shroud 1 (see also FIG. 3). Consistent with aerodynamicprinciples, these airfoil sections are constructed and arranged toproduce high or low lift through any combination of high or low liftcoefficients, and larger or smaller local chord lengths or angles ofattack. Note that in various embodiments herein, the LTA shroud/craftgeometry can alternatively be constructed and arranged to produce aneutral lift or a small positive net lift so long as the lift derivedfrom buoyancy is sufficient to maintain sufficient suspension of thepower-generating assembly.

In addition, or alternatively, to the higher coefficient-of-lift airfoilsections at the bottom of shroud 1, the shroud can be configured tooperate at a positive angle of attack (α_(shroud)) (FIG. 4), and/or toemploy larger airfoil sections at the bottom relative to those at top(FIG. 5).

A mechanism can be provided to dynamically control the angle of attackof the shroud (α_(shroud)) to provide lower or higher lift as necessarythrough, by way of an illustrative example, dynamic lengthening andshortening of the fore F and/or aft A attachment point harness lines.Such a mechanism can, for instance, comprise one or more mechanicalwinches disposed, for instance, at the juncture 12 where tether 11comprises the separate lines extending to the fore F and/or aft Aattachment points. According to this embodiment, each such winchoperates to selectively shorten the length of the associated lineextending to one or more of the fore F and/or aft A attachment points.Alternatively, such a mechanism can be provided at or proximate the basestation, according to which embodiment it will be appreciated thattether can comprise a plurality of separate lines extending between thebase station and each of the fore F and/or aft A attachment points.

Referring to FIGS. 2 and 6, shroud 1 is configured to produce anasymmetric moment of left and right lateral sections thereof, whichasymmetric moment yields a restoring moment that automatically orientsthe longitudinal axis of shroud 1 (defined along the centerline throughstream tube 3) substantially optimally relative to the prevailing winddirection. This is particularly beneficial for higher frequencyvariations in wind direction, as the shroud 1 will passively“weather-vane” about the base station 10 in conditions of low frequencyvariations in wind direction. Generally speaking, this restoring momentis produced by the asymmetric moment of the left and right shroudsections, which are operating at different “angles of attack” whenshroud 1 is yawed with respect to the prevailing wind direction. Moreparticularly, the airfoil sections of shroud 1 are, in the exemplaryembodiment of the invention, shaped such as to produce a “locallynose-down” moment about the airfoil quarter-chord. In the event of anon-zero yaw angle (θyaw≠0), such as occurs when wind direction shifts,the upwind shroud sections operate at a local angle of attack,α_(upwind)=α_(geometric)+θyaw, which is greater than the downwind shroudsections angle of attack, α_(downwind)=α_(geometric)−θyaw, andsubsequently the upwind shroud sections produce a larger “locallynose-down” moment (M_(u)), than the downwind shroud sections (M_(d)).This asymmetric aerodynamic moment sums to produce a net restoringmoment (M_(restoring)) that points shroud 1 in the direction of thewind.

It will be understood from the foregoing disclosure that the asymmetricmoment described above can be tailored to ensure an appropriate responseto wind variations by employing airfoils with higher or lower momentcoefficient.

While the disclosure heretofore has comprehended a shroud for anairborne wind-turbine, it is contemplated that the inventive shroud can,with only modest modification from the foregoing disclosure, be employedin an underwater environment as part of a water-turbine. According tosuch an illustrative embodiment, the power-augmenting shroud andassociated, enshrouded water turbine can be secured to a suitable base,such as, for instance, a tether or tower, whereby the shroud ispermitted to pivot in the water so as to automatically orient itselfsubstantially optimally relative to a prevailing water direction.

As with the embodiment of the shroud described above for employment in awind-turbine system, the shroud according to this embodiment of theinvention is likewise configured to produce rotation about an axis ofrotation upstream of the center of pressure and substantiallyperpendicular to the longitudinal axis of the shroud, so as toautomatically orient the longitudinal axis of the shroud substantiallyoptimally relative to a prevailing water direction.

Unlike the embodiment of the invention for airborne employment, however,it will be appreciated that the underwater variant is not necessarilyfilled with a “lighter-than-air” gas, although buoyancy of the shroud(including in combination with any enshrouded turbine components) isrequired where the shroud is tethered to a base station. This iscontrasted with embodiments where the shroud is pivotally connected to arigid tower secured to the underwater floor or other substrate, in whichcase buoyancy of the shroud is plainly not required. Further accordingto such embodiments, it is likewise appreciated that changes on theshroud's angle-of-attack can be effected employing other than fore andaft tether attachment points such as heretofore described.

Lighter-than-Air (LTA) Craft for Support of Wind Converters

Reference is now made to further embodiments of the present inventionsuch as illustrated in FIGS. 7 through 14. These other embodimentsdisclose the use of turbines or other wind converters, as supported fromother structures, referred to herein as a craft or a “lighter-than-air”(LTA) craft. Where earlier disclosed embodiments describe the use of anencompassing shroud, the embodiments illustrated in FIGS. 7 through 14disclose other craft for the support of turbines or other windconverters, including, but not limited to, semi-circular structures,winged structures and open structures. The LTA craft structures of thepresent invention provide aerodynamic and buoyant lift; corrective yawmoment (in conjunction with any aerodynamic structures present, and notnecessarily due to an asymmetric moment); and a mounting for a windenergy converter (but not necessarily “around” the turbine). Theseembodiments also illustrate various tether arrangements, in particulararrangements with 1, 2 or 3 (or more) primary tethers; fore and afttether attachment points, and side-side attachment points. In oneembodiment there are employed three primary tethers. Single and multipleturbine arrangements are disclosed and highly variable within ordinaryskill.

Additional features include a tail or other structure which extends theaerodynamic structures (specifically vertical and horizontal stabilizersor control surfaces) substantially downstream of the rest of the craft;winglets or horizontal stabilizers arranged to improve stability androtational damping about a pitch axis; a different mechanism for theactuation of the tether system, which is either on the ground andindependent for each primary tether, or with an actuator at the tetherbridle point which shortens or lengthens the bridle/harness lines toimpart a desired rotation position (pitch, roll) to the craft; differentforms of the wind energy converter such as a single wind turbine,multiple wind turbines, or an aerovoltaic converter.

Reference is now made to FIG. 7 which depicts a craft 31 with a closedperimeter made up of two semi-circles 30A and 30B with a straightsection 32 in between. The top and bottom portions are asymmetric,relative to the mid-plane. In this particular embodiment there are threeturbines 34 that are mounted within the closed perimeter defined bymembers 30A, 30B and 32. FIG. 7 also illustrates a tether system thatemploys three primary tethers extend from the ground station 38 to thecraft 31. This includes tethers 35, 36 and 37. Tether 35 is a foretether with attachment at a fore location of the craft 31. Tethers 36and 37 are respective aft tethers with attachments at an aft location.The aft tether attachments are spaced apart and secured to the craft 31on the left and right sides thereof of the craft 31. In FIG. 7 the threeturbines are schematically illustrated, but can, for example, be asshown at 20 in FIG. 1. The attachment location for the tethers is at anouter surface of the craft. Refer, for example, to the afore-mentionedAmick '453 publication for an illustration of an attachment used at theshroud.

Reference is now made to FIG. 8 which depicts an embodiment similar tothat shown in FIG. 7 but with added aerodynamic structures. Thus, thisfigure shows the craft 31 with the same features as illustrated in FIG.7 wherein like reference numbers are used for common components. FIG. 8depicts a craft 31 with a closed perimeter made up of two semi-circles30A and 30B with a straight section 32 in between. The top and bottomportions are asymmetric, relative to the mid-plane. In this particularembodiment there are three turbines 34 that are mounted within theclosed perimeter defined by members 30A, 30B and 32. FIG. 8 alsoillustrates a tether system that employs three primary tethers extendfrom the ground station 38 to the craft 31. This includes tethers 35, 36and 37. Tether 35 is a fore tether with attachment at a fore location ofthe craft 31. Tethers 36 and 37 are respective aft tethers withattachments at an aft location directly from the base station. The afttether attachments are spaced apart and secured to the craft 31 on theleft and right sides thereof of the craft 31. In this embodiment twoadditional fins 33 (aerodynamic structures) have been added on the topsection of the craft 31 for improved corrective yaw moment for yawstability. Also, two additional winglets 39 (aerodynamic structures)have been added on the respective right (30B) and left (30A) sections ofthe craft, to add additional lift and stabilize the pitch and yawmoment, as needed.

Reference is now made to FIG. 9 which depicts an embodiment similar tothat shown in FIG. 8 but with an alternate tether system. Thus, thisfigure shows the craft 31 with the same features as illustrated in FIG.7 wherein like reference numbers are used for common components. FIG. 9depicts a craft 31 with a closed perimeter made up of two semi-circles30A and 30B with a straight section 32 in between. The top and bottomportions are asymmetric, relative to the mid-plane. In this particularembodiment there are three turbines 34 that are mounted within theclosed perimeter defined by members 30A, 30B and 32. FIG. 9 alsoillustrates a tether system that employs two primary tethers that extendfrom the ground station 38 to the craft 31. In FIG. 9 there is a primaryfore tether 35 and a bridled tether 40 that includes a juncture point 41that splits into bridles 42A and 42B. The additional aerodynamicstructures illustrated in FIG. 9 can also be any combination of fins,winglets, wings, stabilizers, and other known structures, that can beadded to the outer surface of the craft. In FIG. 9 the three turbinesare schematically illustrated, but can be as shown at 20 in FIG. 1.

Reference is now made to FIG. 10 which depicts an embodiment similar tothat shown in FIG. 8 but with still a further alternate tether system.Thus, this figure shows the craft 31 with the same features asillustrated in FIG. 8 wherein like reference numbers are used for commoncomponents. FIG. 10 depicts a craft 31 with a closed perimeter made upof two semi-circles 30A and 30B with a straight section 32 in between.The top and bottom portions are asymmetric, relative to the mid-plane.In this particular embodiment there are three turbines 34 that aremounted within the closed perimeter defined by members 30A, 30B and 32.FIG. 10 illustrates a tether system that employs one primary tether 44that extends from the ground station 38 to the craft 31. In FIG. 10 thetether 44 splits at the juncture point 45 into three separate bridles46, 47 and 48. The tether incorporates a bridle point and bridles,having one attachment point on the fore section (tether 46) and twoattachment points on the aft section (tethers 47 and 48) of the craft.The aft attachment points are located on the left and right sections ofthe craft 31. The additional aerodynamic structures illustrated in FIG.10 can also be any combination of fins, winglets, wings, stabilizers,and other known structures that can be added to the outer surface of thecraft. In FIG. 10 the three turbines are schematically illustrated, butcan be as shown at 20 in FIG. 1.

Reference is now made to FIG. 11 which depicts a further embodiment ofthe present invention employing a novel craft having upper and lowerwing sections. In this particular embodiment there are no side walls (itis not a closed perimeter, as in the previous embodiments). Thus, inFIG. 11 the craft 51 has an upper wing section 50 and a lower wingsection 52. The upper and lower sections are different in structurerelative to each other. For example, the top or upper section may have asmaller cross-section than the bottom or lower section. In thisparticular embodiment there are four turbines 54 that are mountedbetween the upper and lower sections 50, 52. In this embodiment thereare three separate primary tethers 56, 57 and 58 that commonly extendfrom the ground station 59 to the craft 51. FIG. 11 also illustrates thetethers as one fore tether 56 with an attachment point to the craft andtwo aft tethers 57, 58 each with an attachment point to the craft at amore aft location. The aft tether attachments are on respective left andright attachment points 53 and 55 of the craft. This embodiment shouldalso employ fins or other aerodynamic structures (not shown, but similarto those illustrated in FIGS. 8-10) for corrective yaw moment for yawstability.

Reference is now made to FIG. 12 which depicts a further embodiment ofthe present invention employing a novel craft 61 comprised of a singlewing section 62. There are no side walls or “upper” and “lower” section.A single turbine 64 is mounted on top of the wing section 62. In thisembodiment there are provided three primary tethers 65, 66 and 67 thatextend from the ground station 68 to the craft 61. FIG. 12 alsoillustrates the tethers as one fore tether 65 with an attachment pointto the craft and two aft tethers 66, 67 each with an attachment point tothe craft at a more aft location. The aft tether attachments are onrespective left and right attachment points of the craft in a similarmanner to that illustrated in FIG. 11. This embodiment should alsoemploy fins or other aerodynamic structures (not shown, but similar tothat illustrated in FIGS. 8-10) for corrective yaw moment for yawstability.

Reference is now made to FIG. 13 which depicts a further embodiment ofthe present invention employing a novel craft 71 comprised of a singlewing section 72. In this embodiment four turbines 74 are mounted on topof the wing section 72. In this embodiment there are provided threeprimary tethers 75, 76 and 77 that extend from the ground station 78 tothe craft 71. FIG. 13 also illustrates the tethers as one fore tether 75with an attachment point to the craft and two aft tethers 76, 77 eachwith an attachment point to the craft at a more aft location. The afttether attachments are on respective left and right attachment points ofthe craft in a similar manner to that illustrated in FIG. 11.

Reference is now made to FIG. 14 which depicts a further embodiment ofthe present invention employing a craft 81 comprised of a wing structure82. In this embodiment three turbines 84 are mounted on top of the wingstructure 82. In this embodiment there are provided three primarytethers 85, 86 and 87 that extend from the ground station 88 to thecraft 81. FIG. 14 also illustrates the tethers as one fore tether 85with an attachment point to the craft and two aft tether 86, 87 eachwith an attachment point to the craft at a more aft location. The afttether attachments are on respective left and right attachment points ofthe craft in a similar manner to that illustrated in FIG. 11. In thisembodiment there are essentially no side walls and the wing structure isessentially open. The wing can illustratively incorporate a dihedralangle, which improves roll stability. Three wind turbines 84 are shownmounted on top of the wing structure 82. Also of note in this embodimentis the addition of a tail structure 83 with vertical and horizontalstabilizers. It should be clear that the number of turbines provided tosuch an embodiment can be widely varied based upon the size ofindividual turbines employed and the carrying volume/form-factor of thecraft.

Likewise, it is appreciated and expressly contemplated that thedimensions and other geometries/measurements, such as airfoil sectionalthicknesses, chord/radius ratio, and others provided as illustrativeexamples of the above-disclosed embodiment of the airborne variant ofthe inventive shroud are not necessarily applicable to the underwaterembodiment, the dimensions and other measurements of which can be variedaccording to specific applications.

It should be clear that the various embodiments of an LTA craft and/orLTA shroud provide highly desirable platforms for mounting one or morewind-energy converters (e.g. turbines). These shapes allow for neutralor positive aerodynamic lift, via their aerodynamic geometry for greaterstability and overall lift capability. Likewise, these craft effectivelylocate the wind converters at an elevation where they can operate mosteffectively, while allowing relatively quick retrieval for service or toavoid severe weather conditions.

The foregoing has been a detailed description of illustrativeembodiments of the invention. Various modifications and additions can bemade without departing from the spirit and scope of this invention.Features of each of the various embodiments described above can becombined with features of other described embodiments as appropriate inorder to provide a multiplicity of feature combinations in associatednew embodiments. Furthermore, while the foregoing describes a number ofseparate embodiments of the apparatus and method of the presentinvention, what has been described herein is merely illustrative of theapplication of the principles of the present invention. For example, thebuoyant fluid used to inflate the LTA shroud/craft is highly variable,and can include conventional helium, hydrogen mixtures of helium andhydrogen, hot air or another heated gas, or any other fluid thatprovides buoyancy in relation to the surrounding fluid environment.Likewise, while various embodiments show single or multiple tethers onthe fore or aft position of the craft, it is expressly contemplated thatthe number and placement of tethers and/or bridles is highly variable.Thus, while various embodiments describe multiple tethers on the foresection at discrete/different locations, and a single tether at the aftsection, in alternate embodiments, a single tether can be located on afore section and a plurality of tethers can be located atdiscrete/different locations on the aft section. Also additional oralternative tethers can be provided at other locations along the craftor connected to certain structures, such as wings or winglets.Accordingly, this description is meant to be taken only by way ofexample, and not to otherwise limit the scope of this invention.

What is claimed is:
 1. A wind-based power generating system comprising:a wind energy converter for converting wind energy into another form ofenergy; a lighter-than-air craft configured to produce at least one ofneutral net lift and positive net lift to the wind energy converter, thenet lift including a net aerodynamic lift and a net buoyant lift; and atethering system configured to restrain the lighter-than-air craft withrespect to the ground, wherein the lighter-than-air craft defines aninterior volume for containing a lighter-than-air gas, and wherein thelighter-than-air craft has a fore section and an aft section, whereinthe tethering system has at least one attachment point on the foresection of the lighter-than-air craft and at least one attachment pointon the aft section of the lighter-than-air craft, and wherein thelighter-than-air craft is constructed and arranged to generate a stableaerodynamic moment with respect to a yaw axis about a center-of-mass ofthe lighter-than-air craft.
 2. The wind-based power generating system ofclaim 1 wherein the lighter-than-air craft has a cross-sectional shapeat least in part configured as an airfoil.